1. Field of the Invention
The present invention relates to a model engine, and more particularly to a cylinder liner capable of oil storage and lubrication used for a model engine.
2. Description of the Prior Art
FIG. 1 is a schematic view of a conventional model engine. The model engine comprises an engine main body 1. The engine main body 1 is longitudinally provided with a cylinder liner 2. A piston 3 is provided in the cylinder liner 2. The piston 3 is movable in the cylinder liner 2 in the axial direction of the cylinder liner 2. The piston 3 is further connected with a connecting rod 4. One end of the connecting rod 4 is pivotally connected under the piston 3. The connecting rod 4 extends downward to extend out of the cylinder liner 2. The other end of the connecting rod 4 is pivotally connected with a crankshaft 5. The crankshaft 5 is transversely disposed under the cylinder liner 2 and extends out of the engine main body 1. Thereby, when the model engine is running, the piston 3 is reciprocated in the cylinder liner 2 to bring the crankshaft 5 to turn through the connecting rod 4, so that the power generated by the model engine is outputted through the crankshaft 5.
FIG. 2 is a partial sectional view of the cylinder liner and the piston of the conventional model engine. FIG. 3 is a partial enlarged view of the cylinder liner of the conventional model engine. When the model engine is running, the piston 3 must be close contact with the cylinder liner 2 for the energy generated by explosion of the oil film in the cylinder liner 2 to convert into kinetic energy to reciprocate the piston 3, preventing the kinetic energy generated by explosion of the oil film from overflowing through the gap between the piston 3 and the cylinder liner 2. However, when the piston 3 is reciprocated in the cylinder liner 2, the reciprocation of the piston 3 will bear great damping if the frictional resistance between the piston 3 and the cylinder liner 2 is too large. This causes a high temperature and reduces the power output efficiency of the model engine. In order to avoid the aforesaid situation, the inner wall of the cylinder liner 2 is honed to form a plurality of oblique cross groves a. The depth of the grooves a on the inner wall of the cylinder liner 2 is very shallow in the range of 0.001 to 0.002 centimeter. Both Chinese Patent Publication No. 102189502 and U.S. Pat. No. 5,549,086 disclose the method to form the grooves a on the inner wall of the cylinder liner 2. The grooves a formed by honing processing not only keep close contact between the piston 3 and the cylinder liner 2 but also decrease the contact area of the piston 3 and the inner wall of the cylinder liner 2. The ragged surface formed by the grooves a on the inner wall of the cylinder liner 2 has the function to store the oil film so as to increase the lubrication effect and to reduce the frictional resistance to lower the temperature.
For keeping close contact between the piston 3 and the cylinder liner 2, the depth of the grooves a on the inner wall of the cylinder liner 2 is limited to in the range of 1 to 2 micrometers, such that the lubrication effect by storing the oil film is limited.
In view of this, another engine is developed accordingly. FIG. 4 is a partial sectional view of another conventional cylinder liner and the piston. FIG. 5 is a partial enlarged view of the cylinder liner. The outer wall of the piston 6 is provided with a plurality of annular members 7 to accumulate an oil film when the piston 6 is reciprocated in the cylinder liner 2. Through the accumulated oil film, when the piston 6 is reciprocated, a layer of oil film is formed between the piston 6 and the inner wall of the cylinder liner 2 to achieve a lubrication effect so as to lower the damping when the piston 6 is reciprocated. The annular members 7 fitted on the outer wall of the piston 6 cause a gap between the piston 6 and the wall of the cylinder, and they may be degraded and deformed easily to result in the loss of the compression ratio of the engine. The power output efficiency of the engine is reduced, so the engine needs further improvement.
FIG. 6 is a sectional view of a further conventional cylinder liner and the piston. FIG. 7 is a partial sectional view of the cylinder liner. The outer wall of the piston 8 is formed with a plurality of grooves 9. The grooves 9 are adapted to store an oil film. When the piston 8 is reciprocated in the cylinder liner 2, the oil film stored by the grooves 9 forms a layer of oil film between the piston 8 and the inner wall of the cylinder liner 2 to provide a lubrication effect so as to lower the damping when the piston 8 is reciprocated. Because the piton 8 is a movable part, the oil film stored by the grooves 9 is easily flung out by the centrifugal force caused by the reciprocation of the piston 8. Thus, the oil film stored by the grooves 9 cannot continue to provide the lubrication effect. This results in an increase of the frictional resistance to bear great damping during the piston 8 is reciprocated. In particular, when the piston 8 is reciprocated at a high speed, the centrifugal force is greater and the oil film in the grooves 9 is flung out constantly. The grooves 9 are almost impossible to store the oil film, so the lubrication effect is not good. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.